Optical fiber connector system

ABSTRACT

A fiber optic connector system for connecting at least one optical fiber cable mounted near the edge of a planar substrate to a backplane, each optical fiber cable including a plurality of optical fibers and a terminating ferrule, the longitudinal orientation of the optical fibers within the terminating ferrule defining a longitudinal axis and a forward direction, the ferrule having a first longitudinal range of motion x 1  and a ferrule spring element having a longitudinal ferrule spring force f n ,. The optical connector system includes a substrate housing assembly and a backplane housing assembly. The substrate housing assembly is designed to be mounted on the planar substrate and includes at least one ferrule receiving cavity for receiving the optical fiber ferrule, and a substrate housing assembly spring. The substrate housing assembly has a longitudinal freedom of motion with respect to the substrate, the housing assembly spring controlling movement of the substrate housing assembly along the longitudinal axis and having a longitudinal spring force h, wherein  
       h   &gt;       ∑   1   n          f   n                     
 
     The backplane housing assembly defines at least one longitudinal receiving cavity, the receiving cavity having a frontal opening along the first surface of the backplane member and a rear opening along the second surface of the backplane member. A frontal door covers the frontal opening and a rear door covers the rear opening.

RELATED APPLICATIONS

[0001] The present application is a Divisional of commonly-owned U.S.patent application Ser. No. 09/643,333, filed Aug. 22, 2000, which is acontinuation-in-part of U.S. patent application Ser. No. 09/443,713,filed Dec. 1, 1999, and which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to an optical fiber connectorsystem. More particularly, the present invention relates to a connectorassembly for optically coupling a circuit card to a backplane.

[0003] The use of optical fibers for high-volume high-speedcommunication is well established. As the volume of transmittedinformation grows, the use of optical fiber cables including multipleoptical fibers, and of systems using multiple optical fiber cables, hasincreased.

[0004] It has long been desirable to increase the number of fibers thatcan be removably connected within a given space. Until recently fiberoptic interconnects were limited to single or duplex formats utilizingindustry standard connectors, such as the SC, ST, LC, and the like.These solutions are analogous to single end electrical cableterminations prevalent prior to the invention of electrical ribbon cableand mass-terminable IDC connectors.

[0005] Fiber optic terminations currently are evolving from singleterminations to mass terminations. Within the past few years, ribbonizedmulti fiber cables have been developed. In conjunction with these cabledevelopment efforts, multi-fiber mounting ferrules also have beendeveloped.

[0006] The design of traditional electronic cabinets is now beingutilized to accommodate optical and opto-electronic devices. Intraditional cabinet designs, the cabinet comprises a box having aplurality of internal slots or racks, generally parallel to each other.

[0007] Components are mounted on planar substrates, called as circuitboards or daughter cards, which are designed to slide into the slots orracks within the cabinet.

[0008] As with electrical cables, the need exists to provide a means toallow the fiber signals to be passed through the backplane of electroniccabinets. A backplane derives its name from the back (distal) plane in aparallelepipedal cabinet and generally is orthogonal to the board cards.The term backplane in the present invention refers to an interconnectionplane where a multiplicity of interconnections may be made, such as witha common bus or other external devices. For explanation purposes, abackplane is described as having a front or interior face and a back orexterior face.

[0009] An example of a backplane connectivity application is theinterconnection of telephone switching equipment. In this application,cards having optical and electronic telecommunication components areslid into cabinets. The need exists to have a removable fibertermination from both the front side and the back-side of the backplane.

[0010] Furthermore, as a function of inserting and removing an opticaldriver card from a rack coupled to the backplane, coupling anduncoupling of the optical connections in the card is to be completed ina blind mating manner.

[0011] In order to maintain appropriate transmission of light signals,optical fiber ends are to be carefully aligned along all three movement(x, y, and z) axes, as well as angularly. Alignment challenges increaseand tolerances decrease geometrically as the number of optical fibers tobe aligned increases. Blind mating of a card-mounted component to abackplane connector has been found to create special challenges withregards to alignment and mating force issues along the axis ofinterconnection.

[0012] For the purposes of the present description, the axis ofinterconnection is called the longitudinal or x-axis and is defined bythe longitudinal alignment of the optical fibers at the point ofconnection. Generally, in backplane applications, the longitudinal axisis collinear with the axis of movement of the cards and the axis ofconnection of the optical fibers in and out of the cabinets. The lateralor y-axis is defined by the perpendicular to the x-axis and the planarsurface of the card. Finally, the transverse or z-axis is defined by theorthogonal to the x-axis and the backplane surface. The angularalignment is defined as the angular orientation of the card with respectto the x-axis.

[0013] In preferred embodiments, the motion of sliding the card into areceiving slot simultaneously achieves optical interconnection. The“optical gap” distance along the longitudinal axis between the opticalfiber ends and interconnected optical components is an importantconsideration. A large gap will prevent effective connection, therebycausing the loss of the optical signals. On the other hand, excessivepressure on the mating faces, such as that caused by “jamming in” acard, may result in damage to the fragile optical fiber ends and matingcomponents. Traditional optical gap tolerances are in the order of lessthan one micron.

[0014] Current connector assemblies include forward biased springmounted ferrules. The purpose of the said bias springs is twofold, one,to absorb a limited amount of over travel of the ferrules during matingand two, to provide a predetermined spring biasing force thus urging theferrules intimately together when the ferrules are in their matedposition.

[0015] An additional subject of concern is card gap, especially whendealing with backplane connector systems. Card gap is defined as thespace remaining between the rear edge of a circuit card and the interioror front face of the backplane. In general, designers and users ofbackplane connection systems find it exceedingly difficult to controlthe position of a circuit card to a backplane within the precision rangerequired for optical interconnects. Card gap, otherwise defined as cardinsertion distance, is subject to a multiplicity of variables. Amongthese variables are card length, component position on the surface ofthe card, card latch tolerances, and component position on thebackplane.

[0016] Over insertion of a circuit card relative to the interior surfaceof a backplane presents a separate set of conditions wherein thebackplane connector's components are subjected to excessive compressivestress when fixed in a mated condition. In certain instances the saidcompressive stress may be sufficient to cause physical damage to theconnector's components and the optical fibers contained therein.

[0017] The need remains for a connector system that prevents componentdamage due to excessive operator force, compensates for longitudinalcard misalignment, yet provides accurate control of optical gap distanceand mating force.

[0018] Another consideration is radial misalignment of the card. When anoperator inserts a card on a slot, it is often difficult to maintain thecard edge perfectly aligned in parallel with the lateral axis of thebackplane. FIG. 1 illustrates an angularity misaligned card 10 having aconnector 12 mating to a backplane connector 14. The card is otherwisecorrectly aligned along the y and z-axes. At the point of contactbetween connectors 12 and 14, the angular misalignment prevents correctgap spacing between optical fibers 16 and causes undue pressure on oneend of the connector and the respective optical fiber end faces.

[0019] Other considerations exist in backplane interconnection systemsother than correct alignment. With the advent of laser optical signalsand other high-intensity light sources, eye safety is a major concernassociated with backplane connector users today. The safety issues arefurther escalated by the fact that ribbonized fiber arrays present agreater danger than the single fiber predecessors because the amount oflight is multiplied by the number of fibers.

[0020] Previous systems, such as that discussed in U.S. Pat. No.5,080,461, discuss the use of complex door systems mounted onterminating fiber connectors, but mainly for the purpose of preventingdamage or contamination of fiber ends. As the lighttransmitting core ofa single mode fiber measures only ˜8 microns in diameter, even a minuteaccumulation of dust particles may render the fiber inoperable. However,prior systems require complex terminations at each fiber end and onlymay be mated to another corresponding male-female connector pair, not tostandard connectors, making their use cumbersome.

[0021] EMI (electromagnetic interference) control also has arisen as anissue in backplane connector design. As connection of optoelectronicdevices through a backplane often necessitates forming of a physicalopening through the backplane of an electronic cabinet, the potentialexists for EMI leakage through the said backplane. Electricalinterconnection has attempted to address this problem through the use ofseveral elaborate EMI shielding techniques. However, current opticalfiber connectors have failed to satisfy this concern.

[0022] Finally, another concern regarding backplane optical connectorapplications is bend radius control. Horizontal cabinets connections areoften subject to bend stresses due to gravity, operator misuse, orphysical constraints, such as when a cabinet is pressed against a wall.Optical fibers are made of glass and rely on total internal reflectionto transmit light signals. When an optical fiber is bent beyond acertain critical angle, fractures may appear in the glass, causing thefiber to break or become damaged. Also, at certain bend angles, even ifthe glass fiber does not break, the optical signal may be lost or maydeteriorate, as the complete light signal is no longer contained insidethe fiber.

[0023] Several methods and apparatus for controlling the bend radius ofan optical cable have been attempted. Among those are preformed bootsthat are slid over the cable, external devices such as clips or clamps,and elaborate injection molded components that are shaped such that whenattached to a cable, the cable assumes the shape of the moldedstructure.

[0024] Since backplane connection frequently involves connecting anincreasing number of optical fibers in a small space, the need existsfor an apparatus for controlling the bend radius of the optical fibers.

SUMMARY OF THE INVENTION

[0025] The present invention relates to an optical fiber interconnectsystem that provides longitudinal and angular alignment control,contamination control, visual safety and bend radius control. In certainembodiments, the optical interconnect system of the present inventionprovides for interconnecting arrays of optical fiber cables in aindividual or collective fashion.

[0026] The fiber optic connector system of the present invention isdesigned for connecting at least one optical fiber cable mounted nearthe edge of a planar substrate, a card, through a backplane. Eachoptical fiber cable includes a plurality of optical fibers and aterminating ferrule, the longitudinal orientation of the optical fiberswithin the terminating ferrule defining a longitudinal axis and aforward direction towards the backplane. Each optical fiber cable isterminated by a ferrule having a first longitudinal range of motion x₁with respect to a retaining member and a ferrule spring element having alongitudinal ferrule spring force f_(n).

[0027] The optical connector system comprises a card housing assemblyand a backplane housing assembly. The card housing assembly is mountedon the planar substrate or card and includes at least oneferrule-receiving cavity for receiving the optical fiber ferrule. Thecard housing assembly includes a card housing spring. The card housingassembly has a longitudinal range of motion x₂ with respect to the card,the card housing assembly spring controlling movement of the cardhousing assembly along the longitudinal range of motion. The card springhas a longitudinally directed spring force h, wherein${h > {\sum\limits_{1}^{n}f_{n}}},$

[0028] that is, the spring force of the card spring can counteract theopposite spring force of all the ferrule springs. It should beunderstood that the ferrule spring may comprise one or more individualspring elements. In one embodiment of the present invention, the cardspring includes two or more springs laterally spaced from in each other,to create an independent card suspension that compensates for angularmisalignment along the x-y plane.

[0029] The backplane member has a first surface and a second surface.The backplane housing include at least one longitudinal receivingcavity, matching a respective cavity in the card housing assembly. Thereceiving cavity has a frontal opening along the first surface of thebackplane member and a rear opening along the second surface of thebackplane member. A frontal door covers the frontal opening and a reardoor covers the rear opening. In a particular embodiment, the doors arespring elements made of a flexible, conductive material and biasedtowards a closed position. To provide EMI protection, the doors may beelectrically connected to ground. In another particular embodiment, thebackplane housing comprises two members, one coupling to the first sideof the backplane and the second coupling to the second side of thebackplane. To provide EMI protection, one of the members may include anelectrically conductive material electrically connected to ground.

[0030] The interconnect system also may include one or more opticalcables including a bend radius control member for controlling the bendradius of an optical fiber cable. The bend radius control membercomprises a deformation resistant heat-shrinked outer jacket wrappedaround the optical fiber cable, wherein the heat-shrunk outer jacket hasa desired bend radius curvature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a side elevation view of an angularly misaligned cardand a backplane connector.

[0032]FIG. 2 is an isometric cut-away view of a first embodiment of aconnector system in accordance with the present invention in a coupledcard position.

[0033]FIG. 3 is an isometric view of the connector system illustrated inFIG. 2 in an uncoupled card position.

[0034]FIG. 4 is an exploded isometric view of the connector systemillustrated in FIG. 2.

[0035]FIG. 5 is an isometric cut-away view of the backplane housingassembly of the connector system illustrated in FIG. 2.

[0036]FIG. 6 is an isometric view of the card housing assembly of theconnector system illustrated in FIG. 2.

[0037]FIG. 7 is an isometric view of the card-facing face of the housingassembly of the connector system illustrated in FIG. 2.

[0038]FIG. 8 is a side elevation view of a backplane connection systemwherein the connector components are aligned along the axis of theinterconnection even though the circuit card is angular with respect tothe said axis of interconnection.

[0039]FIG. 9 is an isometric view of the plug portion of the connectionsystem illustrated in FIG. 4.

[0040]FIG. 10 is an isometric exploded view of plug illustrated in FIG.4 showing the plug fully assembled except for the installation of thecover.

[0041]FIG. 11 is an isometric view of the plug illustrated in FIG. 4with its cover being installed.

[0042]FIG. 12 is an isometric view of the plug illustrated in FIG. 4fully assembled.

[0043]FIG. 13 is an isometric view of the plug assembly illustrated inFIG. 11 wrapped about a forming fixture.

[0044]FIG. 14 is an exploded isometric view of a backplane housingassembly.

DETAILED DESCRIPTION OF THE INVENTION

[0045]FIGS. 2 and 3 illustrate an embodiment of an optical interconnectsystem 100 in accordance with the present invention. The opticalinterconnect system 100 couples a circuit card or daughter card 102 withand through a backplane 104. The card 102 is a planar substrate, such asa circuit card or daughterboard, which may include optical,optoelectronic, and electronic components. The card 102 may be slideablyinserted in a slot defined by card guides 106. The backplane 104includes a through opening 108, a first interior surface 110 and asecond, exterior surface 112.

[0046] The optical interconnect system 100 includes a backplane housing120 disposed within opening 108. The backplane housing 120 includes, inthe present embodiment, a first portion 122 and a second portion 124.The first portion 122 includes male locating features 126 that engagewith corresponding female features (not shown) on a rear face of thesecond portion 124. Locating features three help ensure accuratealignment between the backplane housing portions 122 and 124 duringassembly. It should be understood that in alternative embodimentshousing portions 122 and 124 do not need to be separate and could bemolded as one piece. Splitting off the housing portions 122 and 124,however, may allow for more freedom in mold core design.

[0047] In the present embodiment, fasteners 128 secure the backplanehousing assembly 120 to the backplane 104. Fasteners 128 includethreaded metal inserts inserted through matching bores 130 in the firstand second portion 122 and 124 of the backplane housing 120. Thoseskilled in the art will readily appreciate that mounting screws are usedin conjunction with fasteners 128 and that a variety of fasteningmechanisms, adhesives, interference fitting, and other devices known inthe art may be used to align and secure the backplane housing assembly120.

[0048] The backplane housing assembly 120 defines an array of fourreceiving cavities 132. Alternative embodiments may include a singlereceiving cavity or any other necessary number of cavities toaccommodate various optical fiber cable connections. Each one of thecavities 132 includes a front opening 134 and a rear opening 136. Forthe purpose of the description of the present invention the terms rear,front, forward or backward are merely illustrative to help describe thedepicted embodiments with respect to the figures. The folding frontdoors 138 are coupled to close the front opening 134 and rear doors 140are coupled to close rear openings 136. The front and rear doors 138 and140 in the present embodiment include flat spring metal members hingedlycoupled to the front and rear openings 134 and 136. The doors 138 and140 are designed to fold down flat when a plug is inserted into theopening of the receiving cavity 132. In the present embodiment, thebackplane housing assembly 120 comprises molded plastic pieces of adielectric material that exhibit the structural strength and dimensionalstability required to maintain control of the optical fiber's position.Such materials include, but are not limited to, thermoplastic injectionmoldable polymers that are filled or unfilled with reinforcement agents,and transfer moldable polymers such as epoxy. The doors 138 and 140 aremade of a conductive metal material, such as tempered stainless steel,beryllium/copper alloys or other materials, and are coupled to provide agrounding electrical path. The doors 138 and 140 provide threefunctions:

[0049] 1) to provide a physical barrier to limit ambient contaminationfrom entering the assembled connector housing,

[0050] 2.) to absorb and route to ground electric magnetic interferencethat may otherwise leak through the cavities 132 through the backplane104; and

[0051] 3) to provide eye safety from emitted light signals from eitherend of the backplane.

[0052] The backplane housing assembly 120 may include mating featurescorresponding to common plugs or ferrules. The dual door design allowsfor the sealing of the optical connection without the need to includespecial gated terminations at each connector. The double doorarrangement also allows for at least one door to be closed any time areceiving cavity is not filled by both a rear and a front plug. Finally,the use of conductive metal doors retained in a conductive housingassembly 24 allows for the containment and grounding of EMI components,using a relatively simple and elegant design. In embodiments where theuser is not concerned with any of the above issues, the use of doors maybe optional without effecting the performance and function of thebackplane housing assembly 120.

[0053] Another useful feature of the housing assembly 120 is the use ofside latch receiving features 142. While traditional plug retainingfeatures, such as that in a conventional phone plug, are placed on topof a connector plug and receiving housing, it was found that such anarrangement unnecessarily interfered with the stacking of ribbon flatoptical fiber cables. The present invention addresses this problem byplacing the latch receiving features along the same plane defined by theoptical fiber array in an optical fiber ribbon cable. This allows forvertical stacking of a number of flat ribbon cables in a reduced space.

[0054] The front end of the backplane housing assembly 120 mates with aboard housing assembly 150 when the card 102 is slid into the guideslots 106. The board housing assembly includes a housing member 152,including hollow protrusions 154 shaped in size to correspond and fitinto front openings 134 of the backplane housing assembly 120. The boardhousing assembly 150 includes board attachment features 156 having abarbed end 158. The board attachment features 156 are designed to beinserted through a receiving slot 160 in the planar substrate 102. Whilethe board attachment features 156 secures the board housing assembly tothe board in the transverse and lateral direction, a range of freedom ofmovement along the longitudinal axis is allowed. The present embodiment,the length of the slot 160 exceeds the width of the alignment feature156. Those skilled in the art will be readily aware of additionalmethods for attaching the board housing assembly 150 to the planarsubstrate 102, while allowing freedom of movement in the x direction.Alternative embodiments may include attachment means such as mechanicalfasteners, spring clips or the like.

[0055] The protrusions 154 in the present embodiment are hollow andrectangular shaped and are terminated in a truncated pyramid shaped lead162. The pyramid shaped lead 162 allow for compensation of certainmating misalignments by directing the board housing assembly protrusions154 into the receiving cavities 132 of the backplane housing assembly.Furthermore, the protrusions 154 are shaped to provide alignment withrespect to the inside walls of receiving cavities 132. Protrusions 154also provide an automatic pressure for opening front doors 138 duringmating. The inner walls of protrusion 154 define a stepped cavity 164that provides guidance to a fiber optic ferrule 170 to be seated insideof the stepped cavity 164. The present embodiment, the stepped cavity164, is shaped to receive an industry standard ferrule, such as theMT-Style optical ferrules. Step cavity 164 is designed in such a mannerthat it comprises a front and a rear rectangular opening 166 and 168,respectively. The front opening 166 is sized to allow insertion of theferrule 170 up to an internal flange 172. A typical MT-style connectorincludes a ferrule 170 mounted on a stalk of optical fibers 174,slidably connected to a detente body portion 176. The ferrule 170 has alimited range of motion x₁ along the longitudinal axis. The stalk ofoptical fibers 174 is allowed to move with respect to the detente bodyportion 176. A spring element located between the ferrule and thedetente body portion forward biases the ferrule towards a forward end ofthe range of motion.

[0056] In the present embodiment, the board housing assembly 150includes rear openings 168 designed to accept the MT connector,including the detente body portion 176. The detente body portion 176 isretained against flange 173 while the ferrule 170 is allowed to extendinside of protrusion 154 up to and through the rear opening 168. Thedetente member 176 is designed in such a manner that as the member 176is inserted into the front of the stepped cavity 164, the spring 178 iscompressed between detente member 176 and the ferrule 170. The ferrule170 is prevented from travelling freely through the rear opening 168 bya flange 180 formed in the ferrule 170. The flange 180 is formed to actas a travel stop for the ferrule 170 when flange 180 is engaged withinternal flange 172. The detente member 176 is provided with a latchfeature that engages the rear opening 168 of the board housing assembly150. Preferably, latching features are provided on both side surfaces ofthe housing assembly 150 and the detente member 176. It may be desirablein some instances to remove detente member 176 from the housingassembly, and for these situations, a release feature is provided in theside of the housing. This release feature is cantilevered and allowed topivot and thereby allowing the release feature to be sprung outwards torelease the corresponding latch feature.

[0057] The length of travel of the card 102 along the card guides 106 isselected such that when in the coupled position the board housingassembly 150 exerts spring force on the backplane housing assembly 120.In a preferred embodiment, the width of the card gap should be greaterthan 0, preferably greater than the combined travel of the spring biasedferrules (typically 1 to 2 mm) relative to their respective housings.

[0058] The range of motion x₂ of the board housing assembly 150 withrespect to the card 102 is sufficient to correct for tolerance errors inthe range of movement of the card 102 along the card guides 106, and toabsorb any excessive force imparted by the user when sliding the cardbefore the card is stopped by the backplane housing 120 or by the stopfeatures if present in the card guides 106. The present inventionaddresses issues or overcompression by allowing the circuit card'sattached connector components to move relative to the said circuit card.Accordingly, in the coupled position, the board housing assembly 150 isheld tightly against the back of the backplane housing assembly 120 andis subject to a constant spring bias provided by spring assembly 184.The advantage of providing the constant spring bias is to ensure thatintimate contact is maintained between the housing assemblies 150 and120 even in the event that the card 102 is subject to movement duringits operation.

[0059]FIG. 5 illustrates a detailed cutaway view of backplane housingassembly 120 having front and rear doors 138 and 140. The doors 138 aredesigned such that when the protrusions 154 of board housing assembly150 are inserted into the front opening 134, the pyramid shaped lead 162of the protrusions 154 forces the front door 138 to fold down.Similarly, when a plug 190 is inserted into rear opening 136, theinsertion of the plug 190 causes rear door 140 to fold down. Doors 138and 140 are preferably formed of a spring-like material that withstandsnumerous cycles of being folded to an open position and then returningto a closed position when the plug 190 or protrusion 154 is removed. Ininstances where EMI protection is a concern, the rear doors 140 and thefirst portion 124 of the backplane housing may be constructed of aconductive material such as metal. When made of a conductive material,the rear door 140 and the first portion 124 will absorb the majority ofany EMI radiation that would otherwise escape through the cavities 132.The first portion 124 is then electrically coupled to a ground endfeature. In alternative embodiment, either the doors 140 or the firstportion of the backplane housing 122 may be constructed of a dielectricmaterial, leaving only one conductive element. The remaining conductiveportion would then be coupled to ground.

[0060] By providing both a front door 138 and a rear door 140 coveringboth the front opening 134 and the rear opening 136, the removal ofeither plug 190 or the card housing assembly 150 results in the closingof one of the doors, thus alleviating any possible visual safety risk.It should be understood that each door is allowed to functionindependently of the other. Accordingly, that means that if only oneplug 190 is inserted into the rear opening 136, the rear doors 140 ofthe remaining receiving cavities 132 will remain closed. To furtherassure the tight fit of the doors 138 and 140 within the openings 134and 136, frame features 144 may be formed on the side walls of thereceiving cavities 132 that match the side profile and overlap the sideedges of doors 138 and 140. This further creates a tighter seal toprevent contamination, contain EMI, and prevent light leakage.

[0061]FIGS. 6 and 7 illustrate the positioning of springs 184 insertedinto spring receiving openings 186 and housing assembly 150. Springs 184are wire springs having a wire diameter sized such that the wire springs184 provide a slight pressed fit between the spring, board attachmentfeatures 156 and the receiving boards slots 160. With springs 184inserted into the spring receiving openings 186, the board attachmentfeatures 156 are prevented from flexing, thereby locking the housingassembly 150 to the card 102. Referring in particular to FIG. 6, one mayappreciate how slots 160 provide passage through card 102 for the boardattachment features 156. The barbed end 158 of the board attachmentfeatures 156 is designed as to grip the back side of card 102 therebysecuring the housing assembly 150 along the transversed axis to thedaughtercard 102. The slots 160 are sized such that the board housingassembly 150 has a range of movement x₂ along the longitudinal axis onthe surface of the card 102. The combination of the forward bias of thespring assembly 182 and the freedom of movement x₂ of the housingassembly 150 allows to compensate for incorrect tolerances in thealignment of the card 102 with respect to the backplane 104. Thecombined force of the springs 184 of spring assembly 182 is selected tobe greater than the summation of all opposing spring forces such asthose of the independent springs 178 of the individual ferruleassemblies. Otherwise, the combined force of the springs 178 of theferrule assemblies would push the housing assembly backwards thuspreventing the desired coupling between the board housing assembly 150and the backplane housing assembly 120. However, as the forward movementof the board housing assembly 150 will be limited by flange 151, theindependent ferrules still retain their range of movement, thus assuringa tight fit on each individual optical cable connection.

[0062] As illustrated in FIGS. 6 and 7 the longitudinal movement of theboard housing assembly 150 is controlled by a spring assembly 182. Theterm spring refers to a resilient or elastic member, such as a coiledspring, a biasing clip, an elastic band, a compression foam, or othersimilar devices known in the art. In the present embodiment, the springassembly 182 includes two spring clips 184 laterally spaced with respectto each other and located generally at the lateral ends of the boardhousing assembly 150. The spring assembly 182 serves three functions (a)to exert a forward force along the longitudinal axis on the boardhousing asse1mbly 150, thus creating a spring bias between board housingassembly 150 and the board 102 that the board housing assembly 150 ismounted on; and (b) to lock the board latching features 156, thuspreventing the board housing assembly 150 from inadvertently beingremoved from the board; and (c) to provide compensation for angularmisalignment of the card.

[0063] The spring assembly 182 preferably biases the board housingassembly 150 towards the front or mating edge of the daughter card, suchthat the board housing assembly 150 is forced to move against theresistance of springs 184 when the board housing assembly 150 is movedby an action opposite to that of the normal force of the springs 184.

[0064] Furthermore, as illustrated in FIG. 8, the placement of the twosprings 184 at laterally spaced locations allows for the correction ofangular misalignments, thus reducing the pressure and possible damage onthe leading edge of the backplane housing assembly 150 and compensatingfor angular misalignment of the port.

[0065] FIGS. 9-11 illustrate the plug assembly 190. The plug assembly190 is designed to receive a conventional MT-style connector ferrule andprovide connectorization features to match the backplane housingassembly 120. Those skilled in the art will readily appreciate that theplug assembly may be molded to receive different types of connectors. Inalternative embodiments of the present invention, the backplane housingassembly may be shaped to receive directly traditional connectorassemblies.

[0066] The plug assembly 190 is comprised of a lower housing member 192and housing cover 194. As explained above, a MT style connector assemblyincludes a ferrule 170, and a ferrule spring 178. The MT style connectoris used to terminate a multi-fiber ribbon cable 196 that is surroundedby a protective jacket 198.

[0067] The lower housing component 192 includes a front opening 200defined by flange surfaces 202, a receiving well 204, and aspring-retaining lip 206. The ferrule 170 has a front portion 171 and aflange 172. The front portion 171 passes through opening 200. However,opening 200 is sized such that the flange 172 is too large to passthrough opening 200 and the flange 172 rests against the flange surfaces202. The end 179 of ferrule spring 178 when positioned properly withinlower housing 192, as seen in FIG. 10, rests within receiving well 204and is compressed between flange 172 and the spring-retaining lip 206.The compression of ferrule spring 178 results in a force being exertedagainst flange 172 and lip 206, therein spring biasing ferrule 170forward through opening 200.

[0068]FIG. 11 illustrates housing cover 194 positioned for attachment tolower housing 192. This attachment is facilitated by placing engagingfeatures 208 of housing cover 194 into engaging cavity 210 present inthe sidewalls of the lower housing component 192. As housing cover 194is rotated in a downward direction, engagement features 208 are trappedwithin engagement cavity 210. As the rotation progresses male snaplatches 212 are engaged with the respective female latch receivingfeatures 214, locking lower housing component 192 and housing cover 194together.

[0069] An opening 216 is provided in lower housing component 192 toprovide a path for strength members 218 to pass through. The strengthmembers 218 are generally present in fiber optic cables and aretypically attached to the housings of fiber optic connectors to relieveaxial stress on the cable's optical fibers.

[0070] The lower housing component 192 also includes cavities 220 intowhich posts 222 of the housing cover 194 are inserted during theassembly procedure to provide lateral locking and alignment of thehousing cover 194 to the lower housing component 192.

[0071]FIG. 12 illustrates plug assembly 190 assembled onto the opticalfiber cable 196 with a bend radius control member 230 installed. Thebend radius control member 230 for purposes of this illustration iscomprised of a shrinkable tubing that has been applied over a rearhousing section 232 of plug assembly 190, the cable's protective jacket198, and the cable's strength members 218. The bend radius controlmember 230 is heated and shrunk into position therein securing cable 196to the plug 190.

[0072]FIG. 13 shows a cable forming device 250 comprising a verticalsupport 255 fastened to a base plate 254 and one or more formingmandrels 256 that are attached to vertical support 252. The radius ofthe mandrels 256 exceeds the critical bend radius for the optical fibercable 196. The angles of the mandrels 256 with respect to each othercorrespond to the expected or desired path for the optical fibber cable196.

[0073] To apply the bend radius control member 230, a shrinkable tubingor jacket 262 is first slid or wrapped over the plug assembly 190 andthe optical fiber cable 196. The term heat-shrinkable jacket or tubingis intended to include tubing, jackets, tapes, wraps or coatingscomprising heat-shrinkable materials that may be wrapped around thedesired portion of the optical fiber cable. The term heat-shrinkablejacket refers to a material that, when heated, collapses and compressesaround the optical fiber cable, and remains in this collapsed shape uponreturning to ambient temperature, such as heat-shrinkable plastics.

[0074] The cable 196 and the shrinkable tubing 262 are wrapped aboutmandrels 256. The illustrated device 250 produces a dual bend whereinthe cable 196 is formed down and left thus creating a compound bend. Theshrinkable tubing is then heated to a temperature sufficient to causethe tubing to shrink. In the present embodiment the heat exposurerequired to collapse the heat-shrinkable material is selected to avoidany detrimental effects to the optical fiber cable, yet to be higherthan the normal operating range for the optical fiber cable. Heatsources may include hot air guns, irradiating heat elements, heatedmandrels or other suitable heat sources. The heating may be done beforeplacing the optical cable 196 on the mandrels 256 or afterwards. Theshrinkable tubing 262 and the cable 196 remain wrapped about mandrels256 while the tubing is allowed to cool. Once cooled, the cable 196 willassume the desired shape and bend radius. The stiffness of the formedcable may be controlled by the thickness and the durometer of thematerial from which the shrinkable tubing is formed.

[0075] In certain instances it may be desirable to coat the innersurface of the shrinkable tubing with a heat activated adhesive thatforms a bond with the protective jacket of the optical cable 196 andwith the rear housing section 232. The bend radius control member may beapplied to any portion of the cable where a bend is expected or desired.Field applications may be performed using a wrapable shrink material anda portable heat source, such as a heat air gun or lamp.

[0076]FIG. 14 shows a backplane housing assembly 120 according to thepresent invention including an alternative embodiment of the foldingfront doors 238 and folding back doors 240. In this case, the structureof the folding front doors 238 and the folding back doors 240 includes apair of substantially equally sized biasing members 242,244 connected byan elongate hinge plate 246 located between the biasing members 242,244and integrally formed therewith. The general appearance of each of thefolding doors 238,240 is that of a V-folded planar element including asubstantially centrally located hinge plate 246 having biasing members242,244 joined at opposing longitudinal edges of the hinge plate 246 andextending outwardly of the same side of the hinge plate 246.

[0077] After installation in the housing assembly 120, the biasingmembers 242,244 of each of the folding doors 238,240 provide closure ateither the front openings 134 or the rear openings 136 of a pair ofadjacent receiving cavities 132. In the embodiment shown in FIG. 14,installation of the folding doors 238,240 requires the placing of afirst latch 248 and a second latch 250 adjacent to each of thelongitudinal edges of the hinge plate 246. The latches 248,250 engage anupper latch seat 252 and a lower latch seat 254 formed as recesses inthe upper and lower faces of an intervening wall 256 between adjacentreceiving cavities 132. With the biasing members 242,244 positioned overe.g. openings 134 of an adjacent pair of receiving cavities 132, thehinge plate 246 being aligned with the intervening wall 256 and latches248,250 positioned to engage the latch seats 252,254, application ofpressure to the hinge plate 246 attaches the folding door 240 to thehousing assembly 120. This provides connection of the folding door 240to the intervening wall 256 by interference-fit between the latches248,250 and the latch seats 252,254. Secure attachment of the hingeplate 246 adjacent to the intervening wall restricts movement of thehinge plate 246 but allows deflection of each biasing member 242,244,independent of the other, during insertion of a plug 190 into areceiving cavity 132 or withdrawal therefrom. Fabrication of biasingmembers 242,244 requires the use of durable material that retains itsshape for repeated cycling between a retracted condition, to allowaccess to a receiving cavity 132 and a closed condition in which abiasing member 242,244 fills an opening 134,136 and presents a barrierto contaminants such as dirt, dust moisture and the like. Preferably thedurable material is a flexible metal, such as a stainless steel alloy, aberyllium/copper alloy or similar springy materials that returnsubstantially to their original shape even after numerous applicationsof shape altering forces.

[0078] It should be noted that this invention is not limited to the useof shrinkable tubing to provide strain relief and bend radius control;however the use of shrinkable tubing offers an inexpensive solution toan otherwise costly problem.

[0079] Those skilled in the art will appreciate that the presentinvention may be used when coupling a variety of optical devices andeven non-optical devices that require precise alignment. While thepresent invention has been described with a reference to exemplarypreferred embodiments, the invention may be embodied in other specificforms without departing from the spirit of the invention. Accordingly,it should be understood that the embodiments described and illustratedherein are only exemplary and should not be considered as limiting thescope of the present invention. Other variations and modifications maybe made in accordance with the spirit and scope of the presentinvention.

What is claimed:
 1. A method for controlling the bend radius of at leasta portion of an optical fiber cable having at least one optical fiber,the method comprising the steps of: a. providing a jacket of a heatshrinkable-material; b. placing the jacket around the portion of theoptical fiber cable; c. bending the portion of the optical fiber cableat a desired bend angle; and d. shrinking the jacket around the opticalfiber cable by the application of heat
 2. The method of claim 1, whereinthe step of bending includes bending the portion of the optical fibercable in at least two curves.
 3. The method of claim 2, wherein thecurves are in different planes.
 4. The method of claim 1, the step ofbending the optical fiber cable comprising the steps of: providing acable forming device having at least one mandrel, wherein the mandrelhas a radius greater than a minimum bend radius for the optical fibercable, and wrapping the portion of the optical fiber cable about themandrel.
 5. The method of claim 4, the cable forming device including atleast two mandrels, wherein the mandrels are attached to differentphases of a support, and the cable is bent in an S-shape having twocurves, the two curves being on different planes.
 6. A bend radiuscontrol member for controlling the bend radius of an optical fiber cablecomprising: a deformation resistant heat-shrunk outer jacket wrappedaround the optical fiber cable, wherein the heat-shrunk outer jacket hasa desired bend radius curvature.